The present invention relates to a catalyst formed by combining a monoorganoamide metallocene and a cocatalyst having alkyl aluminum functionality and to its use in the polymerization of olefins.
In the field of olefin polymerization, there is currently much excitement generated by the employment of catalyst systems prepared by combining various metallocenes with an organoaluminum cocatalyst. Much of the excitement regarding the use of metallocenes and olefin polymerization is a result of the fact that by altering the types of organic groups in the metallocene, one can produce varying effects upon the polymerization process.
The term xe2x80x9cmetallocenexe2x80x9d as used herein refers to those organometallic compounds in which at least one cyclodienyl group is pi-bonded to a metal of Groups IVB, VB, VIB, and VIII of the Periodic Table. A large number of metallocenes are now known, some examples include the metallocenes disclosed in such patents as U.S. Pat. No. 4,937,299; U.S. Pat. No. 5,529,966: and U.S. Pat. No. 5,444,145. In the past the metallocenes which were most often employed in forming polymerization catalysts were those in which the other remaining valences of the metal were satisfied by halogen or hydrocarbyl radicals.
There have been a few references to metallocenes in which the remaining valences are satisfied by dihydrocarbylamide radicals. One example is U.S. Pat. No. 5,529,966 and another is U.S. Pat. No. 5,444,145.
The present invention is based on the discovery that active polymerization catalysts can be formed by combining a cocatalyst having alkyl aluminum functionality with metallocenes in which there is at least one monoorganoamide radical bonded to the metal of the metallocene.
It is considered particularly surprising that such metallocenes would be effective as olefin polymerization catalysts because it is believed that those skilled in the art would have expected that when such a metallocene was combined with a cocatalyst comprising an alkyl aluminum, one would obtain an imine which would dimerize to an inactive metallocene. For example, the article by Walsh, Hollander and Bergman, J. Am. Chem. Soc., 110 (26) 8729-8733 (1988), particularly on page 8730 suggest that when such a metallocene is contacted with an alkyl aluminum, one would expect an alkylation to occur which would form an imine which would dimerize to give an inactive metallocene of the type shown in formula 2a on page 8730 of that article.
In accordance with the present invention, it has been surprisingly discovered that monoorganoamide metallocenes can, in fact, be effective as olefin polymerization catalysts when used with a cocatalyst having alkyl aluminum functionality.
Accordingly, an object of the present invention is to provide a new class of metallocenes that can be employed in the polymerization of olefins.
Another object of the present invention is to provide a new process for polymerizing olefins.
In accordance with the present invention, there is provided a catalyst system resulting from the combination of a metallocene having a monoorganoamide radical bonded to the metal of the metallocene and a cocatalyst having alkyl aluminum functionality. Further in accordance with the present invention, there is provided a process for polymerizing olefins comprising contacting at least one olefin with the inventive catalyst system under suitable polymerization conditions.
The monoorganoamide metallocenes used in the present invention are those in which the monoorganoamide radical is bonded to the metal of the metallocene.
The term monoorganoamide as used herein refers to an amide radical having a hydrogen and an organo group bonded to the nitrogen which is in turn bonded to the metal of the metallocene. The organo group can be selected from any suitable organo group. Generally, the organo group would contain 1 to 20 carbon atoms. One example would be monoalkylamides. Another example would be monoarylamides. Generally the aryl group of the monoarylamide would have 6 to 20 carbon atoms. The aryl group could also have non-hydrocarbyl substituents such as halides. Monoarylamide radicals could also be referred to as anilide radicals.
Some typical monoarylamides are those in which the aryl groups are selected from aryl radicals such as phenyl, 2,6-diisopropylphenyl, 2,4-difluorophenyl, 2,6-dimethylphenyl, 2,3,4,5,6-pentafluorophenyl, 4-tertiarybutylphenyl, 2-methylphenyl, and the like.
The currently preferred metallocenes of the present invention are those of the metals of groups 4b, 5b, and 6b of the Periodic Table. The currently most preferred metals are zirconium, hafnium, and titanium. The metallocene can have one or more of the monoarylamide groups. In metallocenes in which two cyclodienyl groups are bonded to the metal, it is currently preferred for the metallocene to have two of the monoarylamide groups bonded to the metal of the metallocene. Some specific examples of what is meant by monoaryl amide metallocenes include the metallocenes bis(cyclopentadienyl) zirconium bis(2,4-difluoroanilide), bis(cyclopentadienyl) zirconium bis(monophenylamide), bis(cyclopentadienyl) zirconium bis(2,6-diisopropylphenylamide), 1-(cyclopentadienyl)-1-(9-fluorenyl)-1-(but-3-enyl)-1-(methyl) methane zirconium, bis(2,6-diisopropylphenyl amide), bis(1-methylindenyl) zirconium bis(2,6-difluorophenylamide), 1-(indenyl)-2-(9-fluorenyl) ethane zirconium bis(2,6-dimethylphenylamide), bis(cyclopentadienyl) titanium bis(2,3,4,5,6-pentafluorophenylamide), bis(n-butylcyclopentadienyl) zirconium (4-tetrabutylphenylamide) (chloride), bis(n-butylcyclopentadienyl) hafnium bis(2-methylphenylamide), and the like. The monoarylamide groups could also be referred to as monoarylamido groups.
The metallocenes of the present invention can be prepared by reacting a suitable alkali metal salt of a monoarylamide with a respective metallocene which has a halide or an alkyl group bonded to the metal of the metallocene. Examples of metallocenes which can be used as the starting material include those disclosed in U.S. Pat. No. 4,937,299 and U.S. Pat. No. 5,444,145. Examples of such preparations are disclosed in Walsh et al., J. Am. Chem. Soc. 110, 8729-8731 (1988); Wartchow and Doye, J. Organomet. Chem. 566, 287-291 (1998); and Walsh et al., J. Am. Chem. Soc. 114, 1708-1719 (1992).
The cocatalysts that can be employed in the present invention include any suitable organoaluminum compounds containing alkylaluminum functionality. Examples include trialkyl aluminum compounds, dialkyl aluminum halide compounds, dialkylaluminum hydride compounds, alkyl aluminum dihalide compounds, and alkyl aluminoxane compounds. Some specific examples include trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, diethyl aluminum chloride, ethyl aluminum dichloride, ethyl aluminum sesquichloride, diethyl aluminum hydride, methyl aluminoxane, ethyl aluminoxane, and the like.
The currently preferred cocatalyst is an aluminoxane. Such compounds include those compounds having repeating units of the formula 
wherein R is an alkyl group generally having 1 to 5 carbon atoms.
Aluminoxanes, also sometimes referred to as poly(hydrocarbyl aluminum oxides) are well known in the art and are generally prepared by reacting an organo hydrocarbyl aluminum compound with water. The currently preferred cocatalysts are prepared either from trimethyl aluminum or triethyl aluminum, sometimes referred to as poly(methyl aluminum oxide) and poly(ethyl aluminum oxide), respectively. The currently most preferred cocatalyst is methyl aluminoxane, also referred to herein as MAO. It is also within the scope of the invention to use solid forms of the cocatalyst, such as solid methyl aluminoxane that is only sparingly soluble in toluene. One method for forming such a solid aluminoxane is disclosed in U.S. Pat. No. 5,411,925.
The amount of cocatalyst can vary over a wide range. It is currently preferred for the molar ratio of the aluminum in the aluminoxane to the transition metal in the metallocene to be in the range of about 0.1:1 to about 100,000:1 and more preferably about 5:1 to about 15,000:1.
The catalyst system can be prepared by merely combining the metallocene and the cocatalyst in any suitable manner. Typically the two are combined in a liquid in which the metallocene is soluble at a temperature in the range of about 0xc2x0 C. to about 200xc2x0 C., more preferably about 0xc2x0 C. to 40xc2x0 C. It is within the scope of the invention to prepare the catalyst system in the presence of a particulate support such as silica. It is also with the scope of the invention to prepare solid catalyst systems by contacting the catalyst system with an olefin to form a solid prepolymerized catalyst system.
The novel catalyst systems of the present invention can be used to polymerize olefins, especially alpha olefins having 2 to 12 carbon atoms. Often such polymerizations would be carried out in a homogeneous system in which the catalyst and cocatalyst were soluble; however, it is within the scope of the present invention to carry out the polymerizations in the presence of supported or insoluble particular forms of the catalyst and/or cocatalyst. The catalyst is thus considered suitable for solution, slurry, or gas phase polymerization.
The inventive catalyst systems can be used for the polymerization of a wide range of olefins, including alpha olefins having 2 to 12 carbon atoms. They can be used to polymerize ethylene in the presence or absence of other olefins, including dienes. Examples of other olefins that might be present include mono-unsaturated aliphatic alpha-olefins having 3 to 10 carbon atoms. Examples of such olefins include propylene, butene-1, pentene-1, 3-methylbutene-1, hexene-1,4-methylpentene-1,3-methylpentene-1, heptene-1, octene-1, decene-1, 4,4-dimethyl-1-pentene, 4,4-diethyl-1-hexene, 3-4-dimethyl-1-hexene, and the like and mixtures thereof.
The polymerizations can be carried out under a wide range of conditions depending upon the particular metallocene employed, and the results desired. It is considered that generally any of the polymerization procedures used in the prior art with any transition metal based catalyst systems can be employed with the present metallocene inventive compounds.
In many cases, the polymerization would be carried out in the presence of liquid diluents which do not have an adverse affect upon the catalyst system. Examples of such liquid diluents include propane, butane, isobutane, pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, toluene, xylene, and the like. The polymerization temperature can vary over a wide range, temperatures typically would be in the range of about xe2x88x9260xc2x0 C. to about 300xc2x0 C., more preferably in the range of about 20xc2x0 C. to about 160xc2x0 C. Typically the pressure would be in the range of from about 1 to about 500 atmospheres or greater.
The polymers produced with this invention have a wide range of uses that will be apparent to those skilled in the art from the physical properties of the respective polymer.